Control of aquatic plants



Patented June 16, 1953 CONTROLOF AQUATICPLANTS I I Arthur-W. Swezey, Garden Grovacalif assignor to The Dow Chemical .Company, Midland, .Mich., acorporation of Delaware No Drawing. Application October 15, 1949,

Serial No. 121,643

I v 4 Claims. 1

This invention relates to herbicides and is. p

.ticularly concerned with a composition and method for killing aquatic plants. The expression aquatic plants as hereinemployed refers to vegetative organisms normally growing in water and in which the leaf and stemparts are largely submerged. The expression is inclusive of alga such as Chara spp. (stonewort), a vegetativeorganism with stem-like and whorled leaflike structures; waterplants which have no roots such as Ceratophyllum .deme rsum (coontail) and rooted aquatic Weeds such as Anachrm's dense (waterweed), Vallisneria ome'rz'caxna (tape grass), and Potamogeton pectinatus (pondweed).

Aquatic plants growing out of place are commonly considered weeds, and millions of dollars are expended annually for their control. In irriation ditches, canals, riversand streams, these plants hinder the flow of water, cause excessive sedimentation, result in high water loss .from evaporation, and interfere with navigation. In ponds and lakes, they frequently develop such a dense growth as materially to limit the usefulness of such bodies of water for either recreational or commercial purposes. Mechanical. operations, such as dredging, chaining, burning and mowing have heretofore been the principal :means of control. More recently efforts have'been made at chemical control. The shortcomings'of the latter. methods have includedthesuperficial burning of exposed leaves without the killingof rootsso as poisoning of the water so as to makeit unsuited forirrigation purposes, and specificity of action against certain species only, thus leading to increased growth-activity on the part of unaffected plant growth. The desirability of an improved control measure appears evident.

to ermit the quick regrowth of the plants, the

' in-thewide range of Water temperatures over water adjacent .to the submersed portions of I thexane as a principal active toxic ingredient.

' The advantagesaccruing to thenew composi- :tion and to the application of the same for control of aquatic weed are. many. The rapidity :ofsaction is in. striking contrast-to many other herbicide products which frequently requireiup toiseveral weeks-,or more .to. accomplish control of vegetation. .Also, the versatility of action against aquaticgrowths is advantageous in that it permits the simultaneous control of many different kinds of .plants Whether narrow- .or broadleaf, and of all plantparts includingroots. In previous operations with known herbicidal materials against mixedstands of undesired vegetation the killing of one type of, plant frequently has encouraged the growthiof unafiectedplants so as to vitiate the initial results and necessitate multiple treatments with attendant inconvenience and expense. The matter of economy of operation is also of importance. The toxicant material here employed is relatively inexpensive, easy to handle, and effective at-very low dosages. All of these features contribute to the usefulness and desirability of the present development. Also, the presence of very small amounts of delta hexachlorocyclohexane in the water and on dead plant residuesdoes not present aproblem with respect tosubsequent utilization of the water in agricultural operations such asirrigation. The tolerance of all crop plants for water containing delta .hexachlorocyclohexane has not been exactly determined, but it has been found, for example, that the diversion of the water from a treated irrigation ,ditch into the waterof an untreated ditch generallyaccomplishes sufficient dilution that the water'safelycan be used onmost desirable plant species.

A further advantage in the invention resides whichthemethod is O erable. Thus the treatment can be carried out at almost any water temperature which will permit the growth and development of aquatic plants to the point where they becomea nuisance.

The compositions-ofthe present invention are preferably liquid concentrates in which the delta 1,2,3,i,5,6 --hexachlorocyclohexane is associated with (1) adispersing and-emulsifying agent and (2) a mutual solvent 'for the toxicant and emulsifying agent. The balanced composition contains sufficientof the'solvent to prevent the separation of toxicantand-emulsifying agent in the'con'centrate, and sufiicient emulsifying agent to make the composition self-dispersing in waterto give a milky dispersion which thereafter'breaks topermit the settlingout of the solution of the delta hexachlorocyclohexane in the form of small water-immiscible droplets. Also, such composition should be characterized by a density only slightly greater than water.

'The expression dispersing :and emulsifying agent as herein employed refers to one or a combination of complex organic derivatives of the type identified as sulfonic acids, polyesters, polyethers, ether esters, ether alcohols, abietic acid-containing complexes, naphthenates, and certain salts of such compounds which have a relatively high solubility in organic liquids. Illustrative of materials which may be so employed are alkyl-aryl sulfonic acids, alkali metal rosinates, alkali metal naphthenates, sodium alkyl-aryl sulfonates, sorbitol long-chain fatty acid esters, polyalkylene derivatives of sorbitol' long-chain fatty acid esters, polyalkylene oxides, and polyalkylene oxide derivatives of phenolic structures. These materials are as described in Emulsion Technology, second edition, pages 329-346, published 1946 by Chemical Publishing Company, Brooklyn, New York. The proportion of such agent employed is not critical, provided only that the dispersing action be accomplished. Generally, from about 5 to 20 per cent by weight of the total composition is sufficient, depending upon the particular agent selected.

The expression mutual solvent is inclusive of such materials as cyclohexanone, benzene, xylene, isopropyl benzene, hexalin, cresylic acid, isopropyl naphthalene, toluene, various petroleum distillates, and the like. Here again, the proportion may vary widely provided the required solvent and carrier action be supplied. In practice, from about 50 to 90 per cent of such solvent has been found to give desirable results.

Other constituents adapted to be employed in the mixtures include the mono-, di-, and trichlorobenzenes, liquid chloronaphthalenes, and chlorinated alkylbenzenes. Here again, the limiting factors on the ultimate mixture include the indicated characteristics of density and dispersibility' in water.

The proportion of delta hexachlorocyclohexane in the ultimate liquid concentrate composition may vary from about 3 to 40 per cent or higher and is largely determined by the solubilities of the various constituents in the composition.

The liquid compositions are readily prepared by mixing and warming the several constituents. The resulting concentrate should be a mobile liquid adapted to be sprayed or otherwise distributed in conventional apparatus. It has been found advantageous to mix such product with approximately an equal volume of water shortly before application. This permits improved distribution of the toxic ingredient, and facilitates dispersion of the ultimate mixture in the water.

An alternative mode of compounding includes the dispersion of the delta hexachlorocyclohexane in a finely divided carrier such as diatomaceous earth, pyrophyllite, clay, or fullers earth to form a wettable powder. In such mixture, the delta hexachlorocyclohexane -may constitute from 5 to 95 per cent by weight of the ultimate composition, and such wetting and dispersing agents, organic solvents, or supplementary toxicants may be included as may appear desirable. The production of such wettable powders is readily accomplished by simply grinding the materials together. Alternatively, the delta hexachlorocyolohexane and other constituents may be dissolved in a suitable organic solvent and the finely divided carrier wet with the solution. The solvent may or may not be recovered by evaporation as desired.

The method of the present invention contemplates the application of the described materials to any pond, lake, river, stream or ditch Where '4 submersed aquatic plants are a problem. However, the eifective ingredient has been found sufiiciently toxic to fish and other marine animal life that the preferred embodiment is the treatment of drainage and irrigation ditches where the conservation of fish life is not critical. In instances where it is desired not only to control vegetation but also to eliminate fish and other water life, as in the poisoning of trash fish to permit restocking, the treatment of lakes and ponds is strongly recommended. It should further be pointed out that the treatment has not proven completely satisfactory against water hyacinth, although at 500 parts of the toxicant per million parts of water a considerable control is obtained upon the leaves and stems of the plant, and the roots and bulblets exhibit some effect of treatment.

In general, the method of the present invention comprises the killing of aquatic plants by dispersing into the water adjacent to the submersed portions of the plants a lethal concentration of delta 1,2,3,4,5,6-hexachlorocyclohexane. Any suitable formulation of delta 1,2,3,4,5,6- hexachlorocyclohexane may be employed in ponds or lakes, with the water-dispersible liquid concentrates preferred in the treatment of streams, ditches or other moving water.

The application may be made at any suitable water temperature but preferably above 50 F. In ponds or other standing water, minimum operable concentrations range between about 25 and 200 parts of toxicant per million parts of water, depending upon plant species, plant mass, water temperature, exposure time, and other conditions of operation. In moving bodies of water, minimum concentrations should be from 50 to 2000 parts of toxicant per million parts of water, again depending upon operating conditions and plant species concerned. Preferred range of concentrations is from to 500 parts per million. At exposure times of one-half hour and one hour, minimum concentrations of 500 and 250 parts per million, respectively, have been found to give good results.

In application, the object is to provide a relatively uniform dispersion of a lethal concentration of the toxicant in the water adjacent to the undesired plant growth and for an exposure time sufficient to cause the death of the vegetation.

.This is readily accomplished by spraying or dispersing the described concentrate compositions just under the surface of the water and directly above the plant mass so as to accomplish their dispersion and thereafter permitting the toxicant to settle onto the plant surfaces and into the stream or pond bottom about the plant roots. Application may also be made by spraying or sprinkling on the water surface. With the liquid compositions, application may be made with a pump and spray boom assemblage so that the ejected spray or stream of the composition is placed at a point below the surface of the water and just above the vegetation, the expulsion of the concentrate from the orifices of the boom being under such pressure as to accomplish the relatively uniform dispersion of the concentrate in the water. Alternatively, the composition may be sprayed over the surface of the water with suflicient force to accomplish dispersion of the concentrate to form a milky blanket which slowly settles through the water and onto the plant surfaces. With the wettable powders, the composition is dusted on the surface of the water som -.d s ence upst am from the sand. for examination. {Ihere owithisufificient lagitationto insureqwettingg and cil s eamaa itqhe 9! ..z =the eet f=fiowiner ,pndi sra ernnn rie :t th amount em l yed a r e o plie ti n- .Her i. it o s'.-in .o.ducediin oJ growth, and a blanket v of d ine bv-v sue .:;in 1?e ti n- A. on -.-1nQ i.e .ofop ration.=inqlude nt 0du9ee .Qe et b e k apsa s ra e 2 QW 1. 2511 mfeqeza nreierebl -t :the lowe .lev h h Wete e hem l srdisp r iqn Q t XiQa tm Le :siwmth s r am .132 ee ,poi itien z be bse v and e di ee'alw eiint q i ;sieed- Bv;.Qb e -va iQ -1:th ,ntens t oi h el usi disper ion t e "c incentret q b a xicen can.- b eselv e t m te ee venie t techn qu c de pos ti n nee b i h i -discbe bw the surface of the stream an dqacent to the ee tationiunde e tm nt- ;W en th ur d of t was a tr b ta le t meese c o r s- :P. d lta ex ci bi oe o e ane,. is low ,s

as clearly to reveal-the disc,. additionalaconcen- ;tratemay beemployed.-

Among the submersed aquatic weed s which m -be con lled-wi h the des ribed .omrpsi- .tionand method .are water stargrass (Heteranthera dubia) horned pond-weed (Zannichellia m w i an mi io Mvri h him e91 The following examples :illustrate the :invention ut o t l e-eqn truede limltin I casual stirring became evenly distributed throughout the tank. Ifhe dispersion tended'to settle very slowly tothebottqmjof the tank; Theplant as treatedwaspo npletely .submersed in the water and was permitted .to remain in contact with the dispersed concentrate for 1a period of one hour. .Atltheend of this time,

each tank was thoroughlyjflushed and .filledwith fresh water. .51 days after treatment, the vegetative growth was examinedand .an apparent lQO percent top-kill observed. After .42 days,-,the ftankswere drained and the entire plant -lifted o a arent e wthnd th .ent r jnlant 'eiz ee .d

d ebseet me- 1 tanks.

deedandsere with le n-stem androot tissue well 1 on w yt -h qteria deeomp s t on.

Check observations were carried out simultaneously in untreated tanks. "Here the plants flourehe .Wi hQll IlQi0@ Q 1. 9f di:b Q e determinat nath W mqstlyjirq l t 7 F;

- EZXAME i .-;s 1 1- determinations were -'carried out in which growingb'eds'of llallisneria spiralis were subjected to--treatment with the compositiondescribed in Example 1 in such proportion as to provide a concentration-of 250 parts per million of the hexachlorocyclohexane in the water of, the

Again, the plants were exposed to the action of the herbicide for one hour," and the 160 water to ,give a' milky dispersion .which .upon

porarybrowning of the leaf and stem..growth tanks thereafter-flushed and refilled with fresh -water. -The water temperature during the week following-treatmentranged -from' 70 to 73 F.

The plants were examined after 42 daysand a per cent kill of .bothtops and roots was observed. In check determinations, the Wetting agentand cyclohexanone were employed at the same concentration. A 12.5 per cent die-back of leaves followed by regrowth was observed. The -roots were unaffected.

EXAMPLE 3 'In a further; series of treatments, tanks containing Anacharis densa were treated with the com os t o of Exam e} inth mann r p vi uslyd scr ed a in such pr p rt on ast iv a nc ntration of 4 0. parts o t e de a hexachlorocyclohexane per million parts of we.- term the several tanks. After an exposure time of one hour, the tanks were drained, flushed, and refilled with fresh water. Again 100 percent kill of all leaf, stem androots was obtained.

' EXAMPLE 4 .25 parts .byaweight .of :the d lt is mer f '.:2 -,.3, 5fi:hexachlor y lohexan :10 parts o alkvlatediaryl-rpqly eri al ohol: (Triton X7100) and5 parts of xylenewere mixed together to ;-pr oduc,e; a homogeneous concentrate composition.

This mixture was employedwas ,detcribed in Example 1 for the control of vVaZlisneria amerz'cana growing in the sand bottom of fresh water tanks. Five replications of each determination were made. The concentrations, exposure times and .results'obtained'are set forth in the following table.

Table I v p E 32 Days Deltalfllegaohloro- 38 'DaysE 20 Days, 1

1 eye o exane in ercon Percent parts/million Egg Top Kill Top Kill i figg igs? Kill Kill 1 100 100 100 .65. O 1 1 00 1 00 100 02;;25 l 100 100 100 65. 00 1 100 100 100 72. 5 A: 100 100 100 62. 5 -,500. ..1 as 100 100 1 00 70. 0 500 (xylene and Wet- M 50 25 O 0 ting agent only). 'Qheck- 0 0 0 0 'Where the vxylenealone was employed, atern was observed. This was-followed by regrowth at such-arate that by theend of the-observa- ,tion period it, lwas-dimcult to distingu S th .rea ed pl nt rom th tuntree ed checks- The water temperature during the period of observa-- tions varied from about 69 to 78 F.

' EXAMPLE 5 A further determination in which the composition of Example 4 was employed for control of the tape grass (Vallisneriaameric cma), employed lower concentrations of the hexachlorocyclohexane delta isomer. At one hour exposure time, concentrations of 50, 100 and 150 parts per million gave percentage top kills of 90.6, 100 and .100 and root kills of 52.5, 62.5 and 62.5 respectively in days.

EXAMPLE 6 The operations of the preceding examples were carried out using the composition of Example 5 for the control of coontail (Ceratophyllum demersum), a free-floating plant with no roots. The following table sets forth the results obtained on 1 hour exposure:

The plants in the treated tanks quickly browned and at the end of the observation period appeared to be undergoing rapid bacterial decomposition. When mildly agitated, the vegetative sprays of the plant shattered and disintegrated. The average noontime temperature of the water was 75 F. during the period of observation.

EXAMPLE '7 The composition of Example 5 was similarly employed for control of Sago pondweed (Potamogeton pectinatus), la rooted submersed aquatic forming corms on its roots. The'details of operation were substantially those described in Example 1, with an exposure period of 1 hour. The following results were obtained: v

Table III 4 Weeks Parts/Million of 1 Week, 2 Weeks, Number Delta Hexachloro- Percent Percent cyclohexane Top Kill Top Kill afgg ggg of corms Kill Kill The figure on corms was determined by counting of the storage organs on the roots of twelve representative plants.

EXAMPLE 8 T c'ation's'were made, with water temperature running between 66 and 72 F. The exposure'time was '1 hour, followed by flushing of the tanks. A quick browning of the growing tips of the weeds occurred, although the action of the wettable powder was somewhat slower than was the case where water-dispersible emulsions were employed. After about 15 days, the plants were found to have been killed.

EXAMPLE 9 The composition disclosed in Example 4 was employed in the treatment of a fish-rearing pond completely choked with Sago pondweed. The pond was 10 by 20 feet in outer dimension and 10 inches deep. The pond contained many snails and leeches and a few goldfish. The water temperature was 72 F. at time of treatment.

The liquid "herbicide concentrate was sprayed over'the surface of the pond'with a knapsack sprayer and in suchamount as to give a dosage of 100 parts of the delta l,2,3,4,5,6-hexachlorocyclohexane per 1 million parts of water. The

composition quickly dispersed over the surface of the pond, and as the emulsion began to break,

- settled like a blanket through the water. At the end of 4 hours the emulsion appeared to be completely broken andfor the most part to have settled to the bottom.

One hour after treatment all'the plant tops, as viewed from above, had turned brown. At the end of 4 days there was per cent kill of tops and better than 60 per cent kill of runners and roots (as determined by the lifting of a number of plants from the pond bottom). At 7 days, all vegetation appeared to have been destroyed, and to be undergoing bacterial decomposition. The pond was then finished thoroughly.

In addition to the vegetation control, all snails and leeches werekilled by the treatment. Also, the scattered fingerling goldfish were killed.

The pond was observed over a considerable period of time following treatment and a series of flushing operations. The weed and vegetative growth quickly rotted down without any indication of regrowth. A'number of flushings and a standing period of several weeks were required before the pond bottom was sufficiently detoxified EXAMPLE 10 An irrigation ditch one-half mile long, heavily grown up with Sago pondweed, Potamogeton pectinatus, is treated with delta isomer of 1,23,45,6- hexachlorocyclohexane in the water-dispersible form described in Example 4, in order to restore the ditch to its full water carrying capacity. The ditch is characterized by a 15 cubic foot per second flow and a stream velocity of 10 feet per minute to give an actual flow of 6'75 gallons per minute. The herbicideis applied directly to the surface of the water through the orifices of small nozzles attached to a boom connected through a hose to a small power spray rig consisting of a gear pump and gasoline engine. The herbicide is introduced into the ditch at a treating point 300 feet upstream from the congested area and at a rate to give aconcentration of 500 parts of the toxicant per million of water for one hour exposure time over the weedy section. At a point downstream where the milky blanket of the emulsion has been lessened in concentration, more herbicide is added to bring the toxicant up to its original strength. The desirability of such addition is determined by lowering a metal disc into the water and comparing its visibility to a check area of known toxicant concentration. The treated water of the ditch is disposed of by dilution into a larger ditch before being used for irrigation. Within a few days, the pondweed becomes brown in color, starts to disintegrate and settles to the ditch bottom.

EXAMPLE 1 1 Tomato, radish, cauliflower, cabbage, sweet Spanish onion, parsnips, spinach, kidney bean, squash, pea, pepper, carrot, sugar beet, milo, Punjab flax and sweet corn seeds were planted in well fitted and drained seed beds. When the seedlings were seven weeks old, furrows were made immediately adjacent to the seed rows and the plant stands irrigated with water containing the delta isomer of 1,2,3,4,5,6-hexachlorocyclo-' hexane at a concentration of 250 parts per million. The hexachlorocyclohexane was supplied as a water-dispersible liquid concentrate as described in Example 4. Three weeks following irrigation, the plantings were inspected and found not to have been injured by the treatment.

I claim:

A method for controlling aquatic plants which includes the step of introducing into the Water adjacent to the submersed portions of the plants a water-dispersible concentrate comprising as a toxic ingredient the delta isomer of 1,2,3,4,5,6-hexachlorocyclohexane.

2. A method for killing the roots, rhizomes, and other submersed parts of aquatic plants which includes the step of introducing into the water adjacent to the plant a water-dispersible herbicide comprising as a toxic ingredient the delta isomer of 1,2,3,4,5,6-hexachlorooyclohexane, the proportion of toxicant in the concentrate and the dosage employed being such as to provide a lethal concentration of the hexachloro- 10 cyclohexane in contact with the plant surfaces.

3. A method for killing the submersed portions of aquatic plants which includes the step of dispersing into the water adjacent the plants a lethal concentration of the delta isomer of 1,2,3,4,5,6-hexachlorocyclohexane.

4. A method for killing aquatic plants which comprises dispersing in the Water adjacent to the plants a minimum of parts per million of the delta isomer of 1,2,3,4,5,6-hexachlorocyclohexane, and maintaining the submersed portions of the plant in contact with the dispersed hexachlorocyclohexane for a suflicient period to permit the action of the toxicant on the plant.

ARTHUR W. SWEZEY.

References Cited in the file of this patent- UNITED STATES PATENTS Number Name Date 1,996,353 Seydel Apr. 2, 1935 2,110,842 Ressler Mar. 8, 1938 FOREIGN PATENTS Number Country Date 573,712 Great Britain Dec. 3, 1945 576,493 Great Britain Apr. 5, 1946 740,232 France Jan. 23, 1933 OTHER REFERENCES mark, No. 363,600, registered January 3, 1939. 

1. A METHOD FOR CONTROLLING AQUATIC PLANTS WHICH INCLUDES TO STEP OF INTRODUCING INTO THE WATER ADJACENT TO THE SUBMERSED PORTIONS OF THE PLANTS A WATER-DISPERSIBLE CONCENTRATE COMPRISING AS A TOXIC INGREDIENT THE DELTA ISOMER OF 1,2,3,4,5,6-HEXACHLOROCYCLOHEXANE. 